1. Field of the Invention
The present invention is directed to an x-ray apparatus of the type having means for measuring the focus-to-skin distance.
2. Description of the Prior Art
Many radiation protection regulations, which regulate the operation of radiographic and fluoroscopic installations, require an identification of the incident radiation dosage to which a patient is exposed, in order to evaluate the radiation risk to the patient. The incident radiation dosage is the radiation dose present at the surface (i.e., the skin, of the patient). The incident dosage can be calculated in theory using a measuring arrangement including a radiation detector (actinometer) with two measurement fields (areas) arranged concentrically relative to each other, when the focus-to-skin distance is known. The radiation detector is attached to the diaphragm housing of the primary radiation diaphragm of the x-ray apparatus, as disclosed in German OS 24 21 243, so that the relative location of the measurement fields with respect to the focus is known. The incident dosage is obtained by processing the output signals of the two measurement fields in combination an electrical signal corresponding to the focus-to-skin distance. This electrical signal is conventionally obtained using infrared or ultrasound measuring instruments. These types of measuring instruments, however, cannot be used, for example, when the patient is covered with sheets.